Polar lipids are constituent components of some foods, although their quality and quantity vary considerably depending on the food source. Dairy products such as milk and eggs are the richest sources of these polar lipids; the glycerophospholipids are also present in plants such as soybean. Nevertheless, a pediatric subject may need to consume a large amount of bovine milk (˜2,000 ml) to obtain a reasonable amount of polar lipids. In addition, consumption of eggs is also limited in infants and children due to the possibility of allergic reactions to the proteins in eggs. Plants are not a source of some of the polar lipids and in particular gangliosides because they are unable to synthesize sialic acid, a component of gangliosides. Furthermore the quality of polar lipids in plants is totally different than milk polar lipids not only due to the fatty acid profile but also due to the ratio of the individual phospholipid components of these lipids.
Polar lipids, especially those found in milk, are composed of three major groups of lipids:                (i) Glycerophospholipids such as phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylserine (PS), and phosphatidylinositol (PI), and their derivatives.        (ii) Sphingoids or sphingolipids such as sphingomyelin (SM) and glycosphingolipids comprising cerebrosides (neutral glycosphingolipids containing uncharged sugars) and the gangliosides (GG, acidic glycosphingolipids containing sialic acid) and their derivatives.        (iii) Cholesterol and its derivatives.Phosphatidylethanolamine is a phospholipid found in biological membranes, particularly in nervous tissue such as the white matter of brain, nerves, neural tissue, and in spinal cord, where they make up 45% of all phospholipids. Sphingomyelin (SM) is a type of sphingolipid found in animal cell membranes, especially in the membranous myelin sheath that surrounds some nerve cell axons. It usually consists of phosphocholine and ceramide, or a phosphoethanolamine head group; therefore, sphingomyelins can also be classified as sphingophospholipids. In humans, SM represents ˜85% of all sphingolipids, and typically makes up 10-20 mol % of plasma membrane lipids. Sphingomyelins are present in the plasma membranes of animal cells and are especially prominent in myelin, a membranous sheath that surrounds and insulates the axons of some neurons.        
Lactoferrin (LF), an iron-binding glycoprotein, is one of the major multifunctional agents present in human milk. It has the capacity to bind two molecules of iron in a reversible fashion and can facilitate the uptake of iron within the intestines. Further, lactoferrin has been shown to be both bacteriostatic and bactericidal, and it aids in preventing intestinal infections in humans, especially in pediatric subjects. Additionally, human lactoferrin appears to have a positive effect on the symptoms of diarrheal diseases.
Docosahexaenoic acid (DHA) is an omega-3 fatty acid that is a primary structural component of the human brain, cerebral cortex, skin, sperm, testicles and retina. It can be synthesized from alpha-linolenic acid or obtained directly from maternal milk or fish oil. DHA is the most abundant omega-3 fatty acid in the brain and retina. DHA comprises 40% of the polyunsaturated fatty acids (PUFAs) in the brain and 60% of the PUFAs in the retina. Fifty percent of the weight of a neuron's plasma membrane is composed of DHA. DHA is richly supplied during breastfeeding, and DHA levels are high in breastmilk. DHA concentrations in breast milk range from 0.07% to greater than 1.0% of total fatty acids, with a mean of about 0.34%. DHA levels in breast milk are higher if a mother's diet is high in fish. DHA has recently gained attention as a supplement for pregnant women, noting studies of improved attention and visual acuity in children of mothers given DHA during pregnancy. Nevertheless, the majority of pregnant women in the U.S. fail to get the recommended amount of DHA in their diets. A working group from the International Society for the Study of Fatty Acids and Lipids recommended 300 mg/day of DHA for pregnant and lactating women, whereas the average consumption was between 45 mg and 115 mg per day of the women in the study.
Human milk contains a number of components that contribute to the growth and development of the brain in infants. But, cow's milk and many commercially available infant formulas that are based on cow's milk provide only trace amounts of polyunsaturated fatty acids, such as DHA, lactoferrin and polar lipids. Therefore, there is a need to provide a formula matrix that mimics the qualities of human milk by allowing for effective supplementation of lipids and proteins in order to optimize brain growth and development in formula fed infants.
More specifically, there is a need for nutritional compositions that further promote brain development in pediatric subjects. The present disclosure meets this need by providing nutritional compositions comprising the milk polar lipids phosphatidylethanolamine and sphingomyelin along with lactoferrin and docosahexaenoic acid. The present compositions advantageously promote neuronal maturation in pediatric subjects.